Mechanical filter



Jan. 2, 1962 sEucHl HONDA ET AL 3,015,789

MECHANICAL FILTER Filed April 16, 195'? 2 Sheets-Sheet 1 fjylg-llad- -Z7?6g-](-K)- jtgdl Jam 2, 1962 sEucHl HONDA ET AL 3,015,789

MECHANICAL FILTER 2 sheetsl-sheet 2 direction a] 10 mation lwave resonator Fv- 7fc)- ting point Filed April 16, 1957 B fue freguency y United States Pater MECHANICAL ,FILTER Seiichi Honda, Hitachi-shi, ibaragi-ken, and Yuzo Nakazawa, Kawasaki-shi, Kanagawa-ken, Japan, assignors to Toyotsushinki Kabusliki Kaisha (known as Toyo JCommunication Equipment Co., Ltd.), Kawasaki-shi, apan Filed Apr. 16, 1957, Ser. No. 653,190

3 Claims. (Cl. S33-72) This invention relates lto an improvement `of an lelectromechanical iilter.

An essential object of ,this invention is to provide an electro-mechanical lter having a remarkably sharp cutoi frequency characteristic. v

Another object of this invention is to provide an electromechanical iilter yhaving a sufficient mechanical strength while employing members made of relatively weak quartz crystal, having remarkably sharp cut-oit frequency characteristics.

The principle, construction and operation of this invention, together with further objects and advantages thereof, may best be understood by reference to the following descrip-tion, taken in vconnection with the accompanying drawings, in which:

FlG. Mc) is a perspective view of an example of this invention, in which live elements are casca-ded.

FIG. l(-b) is a perspective View showing a modification or the example in FIG. 1(a).

FIG. Z(-a) and FIG. 2.(b) are perspective views showing, respectively, other .modiiications of the examples in FIG. l(a) and FIG. 1(1)).

FIG. 3 is an `equivalent electrical circuit diagram of the examples in FIGS. l(a), l(b), .2(a) and 2(5).

FIG. 4 is a perspective view of an element having the simplest construction of `a further example of this invention. Y Y

FIG. 5 is a schematic connection view of this invention, in which .the elements illustrated in FIG. 4 are used as the essential elements.

FIG. 6r is an equivalent electrical circuit diagram of the example in FIG. 5.

FIG. 7(a) is a perspective view of a part of the example in FIG. 7(1)).

"FlG. 7(b) is `a perspective view of a still further ex ample of this invention, showing the principle of the M- derived type electro-mechanical tilter.

FIG. 7(c) is an equivalent electrical circuit diagram of the example in FIG. 7(1)).

FIG. 8(51) and FIG. 9(11) are perspective views of two other examples of this invention.

FIG. 8(b) and FIG. 9(b) areequivaleut electrical circuit diagrams of the examples 1in FIGS. 8(a) and 9(a), respectively.

LFIG. 9;(c`) iis a perspective view of a modification of .the example in FIG. 9(a).

FEG. l0 is a frequencyattenuation characteristic of the example :in FIG. 8;(151).

Jn vthe drawings, the .same .members .are indicated by the same numerals pr symbols throughout.

v material.

'The members l.1 -and u2rform-the quartz-crystal vibrators, vibrating usually in the longitudinal mode, and the orien- 3,015,789 Patented Jan. 2, 1962 rnice l,tations thereof are selected to accommodate to the desirable frequency and temperature characteristics of the Isaid members. Of course, Idetermination of the orientations and forms of the said members 1 and 2 may Vbe` modified in accordance with the vibration modes such as longitudinal vibration, bending vibration, torsional vibration, thickness vibration, lateral vibration and the like.

The transducer y1 and the resonator Zahave the same form. They are plated on'both the front and rear surfaces thereof, as indicated by oblique lines, to make electrodes on the said surfaces. A solder cone 4 is attached to the vibration nodal point of each said surface -and at these points are soldered supporting lead wires 5 which are the electrical terminal of said electro-mechanical filter. The coupler 3 is connected Ito a point near the nodal point of vibration of the transducer and resonator. In the conventional mechanical til-ter, `for the purpose of obtaining a narrow band pass filter, the sectional larea of the coupler must be selected to be very narrow, thus causing the lter to be mechanically weak.

However, when the connection is made at the point near the nodal point, rather than at the nodal point, as in the case of this invention, use of the coupler having a large sectional area for the narrow band pass lter is made possible. Consequently, even when mechanically weak material such as a quartz crystal is use-d as the coupler, it has strength suicient for practical use. v

The equivalent electrical circuit of the electro-mechanical illter of the tive stage type illustrated in FIGS. '1.(a), 1(5) and FIGS. .2((1), 2(17) `can be `indicated as shown in FIG. 3, in which the members m and s, are, respectively, an equivalent mass and an equivalent ystiffness l.which form a series resonance circuit, the said resonance .circuits being coupled by -a .stiiness s2, yand a transducer having an electromechanical conversion rate 11A being connected with each ofvtwo ends of the resultant equivalent circuit.

The operation and character of the circuit in FIG. 3 .in the case of near resonance Vfrequency will be `described in the following in connection with a `band pass filter.

When the cut-olf frequencies, center frequency, terminal impedance, and damped capacity of the transducer are taken. respectively as L1 .and f1, f0=.\/f 1f1. fr, and Cd, the following equations will be obtained.

When the resonators vibrate in the longitudinaldirection, the equivalent klumped constants m1 and 's1 o f a mechanical resonator of 1/5 Wave length will be given by the `following equations. f

l. mir--psrll where p, E., S1 and l1 indicate, respectively, density, rigidity modulus, sectional area, and length of vibrating direction of the said resonator.

Iquartz crystal piece.

3 The coupling stiffness sz'is determined by the distance between the adjacent resonators, and the dimension and material of the resonator. For instance, if any longitudinal vibration is to be transmitted to the resonator of the next stage, the coupling stiffness sm, will be indicated bythe following equation.

EZSZ

.vibration nodal point of the resonator, the coupling stiffness szb will be indicated bythe following equation.

where G, l2, b2, and t are, respectively, rigidity modulus, length of vibrating direction, width of the coupler and thickness of the coupler illustrated in FIGS. 1(a) and l1(b). l

As will be seen from the Equations 2, 4 and 5, it is easily possible to make the bandwidth narrow or wide by suitable selection of the relative positions between the couplers and resonators, and their dimensions.

` In FIG. 4 is shown a simple electro-mechanical filter AQ of two stage type -according to this invention. lSuch a mechanical filter of the minimum number of stages is simplest in its construction and can be made of a small The electro-mechanical filter illusltrated in FIG. 4 may be used for obtaining an electromechanical filter circuit by combination of electrical circuits 6, 7 and 8 with the said filters Q, as shown in FIG. 5. The said combined circuit can be indicated by the equivalent circuit as shown in FIG. 6, the inductances fand capacitances of the said electrical circuit being, of

course, determined by the bandwidth and characteristic vimpedance of the band pass filter to be constructed.

The above-mentioned electro-mechanical filters of this invention relate to the filters, the equivalent circuits of Y which aref of constant K type and the like. However, the filter f this invention may be applied for the electrovmechaniczil filter such as the so-called M-derived type 'filter having attenuation poles inthe attenuation frequency regions, n

The attenuation per stage in the above-mentioned electro-mechanical filter is generally indicated by the folwwo 4 where wo and ws indicate, respectively, the center angular frequency and S2 value at the attenuation pole.

The smaller the factor m is selected, the nearer the attenuation pole can be brought to the cut-oil frequency, whereby a sharp cutoff attenuation characteristic can be obtained.

When such an elastic piece 9 capable of being vibrated longitudinally as shown in FIG. 7(a) is excited at any point except the end points and center point thereof (i.e. dissymmetrically excited), two kinds of antiresonance frequencies determined by the elemental pieces corresponding to the lengths l1 and l1, are produced.

By combination of the antiresonators 9 as described above with a parallel resonator 10 at the positions corresponding to 1/2 wave length l2, a M-derived type electromechanical lter as shown in FIG. 7(b) can be constructed, the equivalent electrical circuit of the said filter being indicated in FIG. 7 (c).

The pass bandwidths in the circuit in FIG. 7(c) can be, when the bandwidths are narrow, indicated approxi.- mately by the following equations.

Thus, the4 equivalent lumped constants are determined.

When such a resonator 9 capable of Abeing vibrated longitudinally along the length l thereof as shown in FIG. 7(11) is excited at any point except the end points and the center point, (i.e., dissymetrically excited), the equivalent masses m1, m1 and the equivalent stiffness s1, sla of the both elemental pieces corresponding to the lengths 11 and 11l of the resonator 9 will be indicated by the following equations.

l:la M0=Ml1=p1f1tze M.=`Ml1.=p.A.l1. where A1, p, and E1 indicate, respectively, the sectional area, density, and rigidity modulus of the resonator. y

By coupling two of the said antiresonators 9 with a resonator having 1/2 Wave length as shown in FIG. 7(b), the M-derived type filter such as shown in FIG. 7(0) will be obtained.

Furthermore, if sectional area, density and rigidity modulus of the resonator 10 of 1/2 Wave length are indicated, respectively, by A2, p and E2, the following equations will be obtained.

When all parts composing the filter are made of the i In the example in FIG. 8(51), the equivalent circuit thereof being shown in FIG. 8(b), the transducer 11 made of quartz crystal is plated on both surfaces thereof with metal to form two electrodes and a supporting lead wire 12 is soldered to each electrode thereof. The resonators 13 and the coupler 14 are also made of quartz crystal vibrator. The coupling positions between the adjacent resonators should differ in accordance with the vibrating modes of the mechanical filter. However, it is generally preferable to couple the said members at a position somewhat separated from the vibration nodal point so as to obtain a resonator capable of operating as the resonator having two antiresonance frequencies.

The bandwidth can be determined by the relative relations between thecoupler 14 andthe dimension of the resonator 13.

In the case of the electro-mechanical filter illustrated in FIGS. 8(a) and 8(b), it is excited at the position within the width corresponding to the length I3 of the coupler 14 (but, [3ft-lsb), so that when the following stages are successively excited along the said width with a uniform force, two antiresonating circuits are obtained, whereby a circuit similar to the circuit of the M-derived type filter will be obtained.

In FIG., 9(a) is shown a modification of the electromechanical lter illustrated in FIG. 7 (b). the equivalent electrical circuit thereof being indicated in FIG. 9(b).

In FIG. 9(a), the filter is made by combination of the exciter 15 capable of transmitting longitudinal vibration towards the longitudinal direction of the filter, series resonators 16 of 1/2 wave length, and couplers 17 of 1/2 wave length, the said filter corresponding to the combined filter of the series resonators 16 with an antiresonator composed of two elements 18 and 19.

The equivalent electrical circuit of the filter in FIG. 9(11) is shown in FIG. 9(1)), in which the lumped elemental constants corresponding to the resonators 16 and couplers 17 are indicated, respectively, by mB, SB and mc, sc and the equivalent masses and the equivalent stiffnesses of two antiresonators are indicated by m1, m1 and s1 and sla, respectively.

The equivalent electrical circuit additionally contains the factors mB and sB as compared with the normal M-derived type. For the manufacture of constant K type filter by combination of the factors mB, SB with me,

sc, the width h of the resonator 16 should be selected so as to be extremely larger than the width ha of the coupler 17. However, when the difference between the width of the resonator 16 and that of the coupler 17 is not remarkably large, the influence due to the factors mB and SB is not too large, so that the constant K type is not established and the IVI-derived type filter is made possible.

The example in FIG. 9(c) corresponds to the electromechanical filter obtained by shortening the length 14 of the restonator 16 of the example in FIG. Qta). When the filter in FIG. 9(c) is used, the influences due to mB and SB in FIG. 9U?) can be more remarkably reduced.

The characteristic curve in FIG. li) indicates frequency-attenuation characteristic of the M-derived type electro-mechanical filter. The said curve indicates that the frequencies f s and fs have, respectively, attenuation paies.

As will -be clearly understood from the above description, since the transducers and resonators of the electromechanical iilter of this invention are made of quartz crystal vibrator, frequency adjustment in the case of manufacture of the elements become very easy and accurate and, particularly excellent temperature characteristic and aging characters are obtained.

While we have described particular embodiments of our invention, it will, of course, oe understood that We do not intend it to be limited thereto, since many' modiiications may be made and we, therefore, contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of our invention.

We claim:

l. An electro-mechanical wave filter comprising a shaped solitary body having input-and-output transducerplates with at least one intermediate resonator plate and a single rod coupled between said transducer plates, said at least one resonator having two free ends and being coupled from a point of dissymmetry of said resonator intermediate said free ends and separated from its vibration nodal point to said single rod.

2. An electro-mechanical Wave filter as claimed in claim l, fur-ther comprising electrodes on the rear and front surfaces of said transducer plates.

3. An electro-mechanical wave filter comprising a shaped solitary body having input-and-output transducerplates with at least one intermediate resonator plate and a central rod coupled between said plates, said at least one resonator coupled at a point of dissymmetry of said resonator to said central rod, wherein said at least one intermediate resonator comprises a first portion perpendicular to said central rod, second portions parallel to said central rod, said iirst portion being coupled between points of dissymmetry on said second portions.

References Cited in the tile of this patent UNITED STATES PATENTS 1,644,004 Zobel Oct. 4, 1927 1,781,469 Mason Nov. 11, 1930 1,954,516 Bourne Apr. 10, 1934 2,276,013 Bohannon Mar. 10, 1942 2,342,869 Kinsley Feb. 29, 1944 2,345,491 Mason Mar. 28, 1944 2,570,579 Masters Oct. 9, 1951 2,596,460 Arenburg May 13, 1952 2,814,785 Burns Nov. 26, 1957 2,821,686 Eurns Jan. 2S, 1958 2,906,973 Mason Sept. 29, 1959 FOREIGN PATENTS 244,560 Ita-ly Feb. 3, 1926 

